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Su Shi Chun

SURE. Spectroscopic Factors. Su Shi Chun. National Superconducting Cyclotron Laboratory Michigan State University. Where is it?. NSCL at MSU. Shell Model. From experiments, we found that nuclei are more tightly bounded

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Su Shi Chun

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  1. SURE Spectroscopic Factors Su Shi Chun National Superconducting Cyclotron Laboratory Michigan State University

  2. Where is it?

  3. NSCL at MSU

  4. Shell Model • From experiments, we found that nuclei are more tightly bounded  number of protons or neutrons is2, 8, 20, 28, 50, 82, 126 (Magic numbers). • Analogous to electron configuration valence nucleons in a nucleus aremoving in anaverage(mean field) potential of the core (closed shell). nuclear shell structure is different from electron shells, e.g. with strong nuclear force • Each valence nucleon has correspondingn, l and jvalues like electrons. 1d5/2 1p1/2 1p3/2 1s1/2

  5. Shell Model • Simplest shell model  independent particle model nucleons do not interact with core or with each other  limited applications but get the Nobel prize for Meyers and Jensen. • Realistic shell models which are useful to compare to data  must include residual interactions between nucleons and core  two-body and three-body force that are very difficult to includetheoretically • To calculate SF, we use Oxbash by Alex Brown (MSU)

  6. What is Spectroscopic Factor? • Spectroscopic factor describes the configuration of the valence (transfer) nucleon orbitals corresponding to the shell model. • Spectroscopic factors can be calculated byshell model. (Theoretical approach) • To measure spectroscopic factors, one needs a reaction model. (Experimental approach) • SF is a fundamental quantity in shell model and can be used to test other assumptions used in shell model including selection of the interactions used in shell models.

  7. (d, p) Stripping Reaction • Not elastic collision. • The neutron from the deuteron is transferred to the target nucleus. • Unlike collision in classical physics Deal with wave functions. (not particles) • No exact wave functions can be found. • Approximation is needed---ADWA.

  8. Importance of Neutron Spectroscopic Factors in the study of rp(proton capture) • Spectroscopic factors (SF) determine the reaction rates of rp capture • important for analyzing evolution of neutron stars. • The rp process (rapid proton capture process) •  consecutive proton captures onto seed nuclei to produce heavier elements. • It is responsible for the generation • of the heavy elements in the universe.

  9. Importance of Neutron Spectroscopic Factors in the study of rp(proton capture) • Most SFs of the relevant states (excited states) are not available experimentally •  calculated by shell model. • Therefore, it is important to establish the accuracies of these calculations bycomparing experimental spectroscopic factors. • Use MIRROR NUCLEI!!

  10. What is Mirror nuclei? • Assume the coulomb repulsion is small compared with other interactions insides the nuclei! • Proton capture  neutron capture/stripping

  11. Why Mirror nuclei? K35 S35 There are much more information on 35S (mirror of 35K) which is close to the valley of stability. Very little is known about the states in 35K which lies on the rp process path.

  12. Spectroscopic Factors from literatures

  13. Need a consistent method • TWOFNR for Experimental SF • SF_Ex= • Johnson- Soper Adiabatic Approximation to take care of d-break-up effects – Adiabatic 3-bodies model • Use global optical potential with standardized parameters (CH89) • n-potential : Woods-Saxon shape r0 =1.25 fm & a0 =0.65 Oxbash for Theoretical Model

  14. What we have gotten so far For ground state only, SF>0.2 What happen to small SF<0.2 ? Results from Jenny Lee -- 2004 SURE student"

  15. Nuclei we will analyze?

  16. Sensitivity to Different Interactions

  17. What we have gotten more than before Excited states  extent to much smaller SFs !!

  18. Summary • By using a consistent analysis approach, we are able to extract spectroscopic factors of the excited states from different reactions and compare between them • Application of the method to excited states allows comparison of small SF values with theory • The extracted spectroscopic factors are sensitive to different interactions used in shell model calculations • With the newest interaction USDB, the comparisons between experimental and theoretical values is good to within 20% uncertainty for SF as small as ~0.001– the theoretical uncertainties are important in astrophysics network calculations

  19. Thank You! Special thanks : Prof. Chu at CUHK Prof. Tsang at MSU Jenny Lee at MSU

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